1. Field of the Invention
The present invention relates to a semiconductor manufacturing system, and more particularly, to a semiconductor manufacturing system having a vertical reaction tube by which a plurality of semiconductor wafers can be processed at a time.
2. Description of the Related Art
Since a thermal process during semiconductor manufacturing needs considerable time, it is preferable that a plurality of semiconductor wafers be processed at one time. Generally, a wafer loading boat as a wafer loading structure on which a semiconductor wafer can be deposited horizontally and a vertical reaction tube in a pipe shape are used in the semiconductor manufacturing system during the thermal process because the uniformity of the thermal process is affected by the uniformity of the flow of a reaction gas. In the wafer loading boat, slots are formed at vertical interval for supporting the semiconductor wafer, and at least one or two edges of the semiconductor wafer is then fitted in the slots.
However, in such conventional semiconductor manufacturing system, since the semiconductor wafer is supported on its edges which are placed in the slots, a supporting force is concentrated on the edge area of the semiconductor wafer contacting the slots. In a thermal process at a high temperature, a significant supporting force is concentrated on the edges of the semiconductor wafer, as the gravitational stress due to the weight of the wafer and the thermal stress due to the different thermal expansion are applied to the semiconductor wafer, thereby resulting in final mechanical deformation of the semiconductor wafer such as a form of warp, bow and slip. Such mechanical deformation becomes a more serious problem in a large size semiconductor wafer, a diameter of which is 300 mm (12 inches) and higher, and thus reliability of a process is reduced. In order to prevent such mechanical deformation of the wafer due to high temperature thermal processing and to distribute the gravitational and thermal stresses of the wafer evenly, a wafer loading boat capable of supporting an entire bottom or a portion of surface of the semiconductor wafer is needed. However, a semiconductor manufacturing system having an additional supporting means will be complex and involve still incomplete solution to avoid the mechanical deformation despite higher process cost, and a user will have difficulties in loading and unloading the semiconductor wafer.